Danger Inc. - Hacked low level and kernel code on the Danger hiptop (aka T-Mobile sidekick). Good set of
folks and fun technology. I wish them well.

Be Inc. - Worked on the venerable BeOS operating system. Did some file system and kernel work,
most notably hacked together support for the ext2 and NTFS file systems. It was a total blast, and made a lot of good friends. RIP BeOS.

Projects

Hacked on a few projects in my day, one of which is pretty well known in certain circles.

NewOS - A OS project I started years ago and didn't know when to stop. It's reasonably well mature, and even scored a slahdotting and offer to write an article for Dr Dobbs magazine. It has been forked years ago and now forms the kernel for the Haiku project.

Arm Emulator - Hacked a fun little arm emulator. Still needs some work, but it currently emulates a "generic" ARM based system. Good for prototyping a kernel. SVN depot at git://github.com/travisg/armemu.git. Web browseable here.

Apple ][ Emulator - A cheezy little Apple ][ emulator I wrote a long time ago for fun. Source here.
Here and here are a couple of screenshots.